When evaluating hydrocarbon-bearing reservoirs in a geological formation, estimation of hydrocarbon volumes and hydrocarbon saturation may be desirable. Saturation is the volume fraction of pore space (porosity) occupied by the fluid of interest (e.g., water, oil, bitumen, and gaseous species, etc.). These quantities are used for evaluating reservoir quality, and determination of these quantities may be desirable at different vertical depths in a well.
Various well log measurements are used to derive water saturation, Sw, in open hole and/or cased hole environments, such as resistivity and dielectric measurements. However, parameters of particular interest may include hydrocarbon volume, saturation and density. The above-noted approaches commonly infer hydrocarbon saturation by assuming that the volume of pore space not occupied by water is filled with hydrocarbon, i.e., Shc=1−Sw. Formations that include hydrocarbons in the pore space both as gas, such as methane, and liquid are more complicated to evaluate accurately because the composition of the downhole hydrocarbon in terms of its fluid density may not be well known.